Due to the quick technological progress, most of the currently available electronic devices have constantly upgraded power and performance, which also results in increased amount of heat produced by the electronic devices during the operation thereof. In the event the produced heat accumulates in the electronic devices without being timely removed therefrom, the temperature inside the electronic devices will rise to adversely affect the performance of the electronic devices. In some worse condition, the accumulated heat would result in failure or damage of the electronic devices. To effectively solve the problem of heat dissipation in the electronic devices, heat transfer devices with improved heat transfer performance, such as vapor chamber and thin heat pipe, have been successively developed and introduced into market for use with heat sinks to dissipate heat in a more efficient manner.
According to the currently available thin heat pipe structure, metal powder is filled in a hollow portion of a large-diameter heat pipe and sintered to form an annular layer of wick structure on around the inner wall surface of the heat pipe. The heat pipe is then vacuumed and filled with a working fluid before being sealed and flattened to complete a thin heat pipe structure. When the heat pipe is flattened, the annular layer of wick structure formed on around the whole inner surface of the heat pipe would narrow or clog the vapor channel in the thin heat pipe to adversely affect the vapor-liquid circulation cycle therein and accordingly, result in poor heat transfer performance of the thin heat pipe.
Further, the conventional thin heat pipe is manufactured with a pipe having a fixed diameter. More specifically, the conventional thin heat pipe could not be designed into different shapes or have variable pipe diameter, such as having a larger diameter at one end and a smaller diameter at another end or having two ends with identical diameter and a diametrically expanded or narrowed middle portion, in order to meet a user's actual need. Meanwhile, the wick structure in the conventional heat pipe is uniformly and fixedly provided on around the whole inner wall surface of the heat pipe. When the resultant thin heat pipe is curved or bent to change the shape thereof, the annular layer of wick structure, i.e. the sintered metal powder, in the thin heat pipe is also bent and compressed. The bent and compressed portion of the wick structure tends to separate from the inner wall surface of the thin heat pipe to largely reduce the heat transfer performance of the thin heat pipe. Moreover, the wick structure is only formed as an annular layer on around the inner wall surface of the heat pipe without any other changes. Once the heat pipe is flattened, the annular layer of wick structure is also flattened to become two superposed layers in the thin heat pipe. The superposed layers of wick structure have a certain fixed overall thickness, which prevents the heat pipe from being flattened as much as possible. Therefore, the benefit obtainable from the conventional thin heat pipe is limited.
As to the conventional vapor chamber, it usually includes a substantially rectangular case defining an inner space, and a wick structure formed on inner wall surfaces of sidewalls of the case enclosing the inner space. A working fluid is filled in the inner space. One side of the case serves as a vaporizing zone for bearing against a heat-producing element, such as a central processing unit or a south and north bridge chipset, to absorb heat produced by the heat-producing element. The working fluid in liquid phase is heated at the vaporizing zone and converts into vapor phase. The vapor-phase working fluid flows while carries heat to a condensing zone at the other side of the case and is condensed into liquid again. The liquid-phase working fluid then flows back to the vaporizing zone by gravity or via a wick structure provided in the inner space to start another vapor-liquid circulation cycle. In this manner, it is able to effectively achieve the purpose of eliminating temperature gradient and dissipating heat.
While the conventional vapor chamber achieves the purpose of eliminating temperature gradient, it has the disadvantage of not suitable for transferring heat to a distant location for dissipation. This is because the vapor chamber absorbs heat at one side thereof and the absorbed heat is transferred to the other side via vapor-liquid phase transition of the working fluid in the case. In other words, with the vapor chamber, the elimination of temperature gradient is achieved only by transferring heat from one side to another side of the case. Therefore, the vapor chamber is only suitable for large-area uniform heat transfer but not suitable for heat transfer to a distant location.
In brief, the conventional heat transfer devices have the following disadvantages: (1) the conventional thin heat pipe could not be further reduced in its overall thickness, and could not be changed in its diameter, wick structure and shape; (2) the conventional vapor chamber could not transfer heat to a distant location for dissipation and is relatively heavy in weight; and (3) the manufacturing costs of the conventional thin heat pipe and vapor chamber are high.
It is therefore tried by the inventor to develop an improved heat transfer device to overcome the drawbacks in the conventional thin heat pipe and vapor chamber.